United Nations monitors in Syria reported fiery devastation, the smell of death, vacated homes, looted stores and vestiges of heavy weapons on Thursday during a visit to what had been a Sunni-populated village besieged for days by Syrian forces and pro-government militiamen who said they had cleansed it of rebel fighters.

In a preliminary report on their visit to the village, Al Heffa in northwestern Syria, a spokeswoman for the monitors said it appeared to be deserted, except for “pockets in the town where fighting is still ongoing.” Antigovernment activists said Wednesday that Al Heffa’s residents had fled in the face of relentless attacks by the Syrian military.

The siege of Al Heffa became a focal point of the Syrian conflict this week because of fears expressed by United Nations and Western officials that its residents were vulnerable to a massacre. Those fears were elevated after mass killings in other Sunni-populated locales in the past few weeks, suggesting that the uprising against President Bashar al-Assad, which began 16 months ago as a peaceful political protest, has become a sectarian civil war pitting his minority Alawite sect against the majority Sunni populace and other groups.

Anti-Assad activists also reported the extensive use of Russian-made helicopter gunships in the siege of Al Heffa and attacks in the nearby port of Latakia, a relatively new tactic in Mr. Assad’s campaign to crush the uprising and a possible reflection of rebel success in damaging his army’s fleet of Russian tanks. The helicopters also subjected Russia, Mr. Assad’s principal backer, to renewed Western criticism as an abettor of his repression. Russia has insisted that it takes no side in the conflict.

Photo

A member of the United Nations observers mission in Syria walked through a damaged building in Al Heffa on Thursday.Credit
Khaled Al-Hariri/Reuters

The monitors, who are unarmed, were blocked on Tuesday from visiting Al Heffa by angry civilians, apparently from nearby villages populated by Alawites. The Syrian Foreign Ministry announced 24 hours later that the monitors were welcome to visit Al Heffa, which the ministry said had been rescued from armed terrorist groups — the government term for opponents of Mr. Assad’s governing Baath Party.

“The town appeared deserted,” Sausan Ghosheh, the spokeswoman for the United Nations monitor mission in Syria, wrote in the preliminary report. “Most government institutions, including the post office, were set on fire from inside. Archives were burnt, stores were looted and set on fire, residential homes appeared rummaged and the doors were open.”

Ms. Ghosheh wrote that the local Baath Party headquarters had been shelled and “appeared to be the site of heavy fighting.”

“Remnants of heavy weapons and a range of caliber arms were found in the town,” she wrote. “Cars, both civilian and security, were also set on fire and damaged.”

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Monitors viewed the damage in Al Heffa on Thursday. A report said stores were looted and homes abandoned in the village, which was besieged by Syrian forces.Credit
Khaled Al-Hariri/Reuters

She also wrote that a “strong stench of dead bodies was in the air,” but there was no information on the number of casualties.

In Moscow on Thursday, Syria’s ambassador to Russia, Riad Haddad, said at a news conference that Russia was supplying his government only with antiaircraft weapons, not attack helicopters. He was echoing statements made this week by top Russian officials in response to American accusations that Russia had risked deepening the Syrian conflict through its military support of Mr. Assad.

Mr. Haddad also rejected descriptions of the conflict as a civil war, made this week by United Nations and French officials.

“I tell them the civil war exists only in their heads,” he said. “Armed terrorist groups, which receive regional and global support, want to show that there is a civil war in Syria. They are doing this to create a pretext for international interference.”

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Diplomacy aimed at halting the Syrian conflict has faltered despite the rising levels of violence. Kofi Annan, the special envoy of the United Nations and the Arab League, whose peace plan placing the monitors in Syria is widely considered near failure, has sought to convene a meeting of influential countries to press all sides in the conflict to honor a cease-fire.

Reuters, quoting unidentified diplomats, reported that such a meeting might be held on June 30 in Geneva, but there was no confirmation. The United States has said publicly that it opposes Mr. Annan’s inclusion of Iran if there is a meeting.

In the central Syrian town of Rastan, north of Homs, where rebels have defied persistent military efforts to rout them, an activist reached through Skype said the situation had deteriorated in three consecutive days of bombing from land and air. The activist, who identified himself as Morhaf al-Zoaby, said the Syrian forces were using tanks, helicopters, cluster bombs and rockets emitting an unidentified gray-black gas, killing at least four people. It was impossible to verify his account.

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While Syrian defectors and other opponents of Mr. Assad have said before that he has used gas and other chemical weapons in the conflict, those assertions have never been corroborated independently.

But outside rights investigators have compiled evidence that Mr. Assad’s forces and pro-government militias have engaged in reprisal killings, torture, arbitrary detention and the destruction of homes. In a new report, Donatella Rovera, an investigator for Amnesty International who spent weeks in northern Syria, described what she called “systematic violations, including crimes against humanity and war crimes, being perpetrated as part of state policy to exact revenge against communities suspected of supporting the opposition and to intimidate people into submission.”

The Local Coordination Committees, a network of activist groups in Syria, reported what it said was a knife massacre of dozens of people in the Damascus suburb of Homouriya and uploaded to YouTube a graphic video of what it said were victims. Like many other claims in the Syrian conflict made via the Internet, the images could not be authenticated.

A version of this article appears in print on June 15, 2012, on Page A18 of the New York edition with the headline: U.N. Monitors Report Devastation, and Smell of Death, in Syrian Village. Order Reprints|Today's Paper|Subscribe